1. Field of the Invention
The present invention relates to a server and server program and more particularly to a server and server program capable of sharing content information among plural servers connected to a network.
2. Description of the Related Art
Recently, as a protocol which connects personal computers, peripheral machines and household electric appliances at home with one another so as to provide their functions to one another via a network, universal plug and play (UPnP) has been used (see, for example, patent document 1). The UPnP contains UPnPAV which is the definition specification of a device and service relating to control of audio visual (AV) appliances. Using this UPnPAV realizes a server client system which can distribute music and video on the home network.
Wireless local area network (LAN) has prevailed, so that there are many environments which allow not only home access points but also access points provided in neighboring house and apartment rooms to be accessed. For the reason, the wireless LAN is equipped with a function which prohibits any illegal terminal from connecting to the network by means of cryptographic technology such as wired equivalent privacy (WEP). In the above-described server client system, like the wireless LAN, the server is equipped with a function which limits distribution of content data and content information to only clients allowed to access them to prevent the content from being used by any illegal terminals. According to an adopted method in this case, for example, the server does not respond to a discovery action (action for detecting any network appliance) from a client not allowed to access, simple object access protocol (SOAP) action (action for calling data or service in other computer) or a request for content distribution. This method can be applied not only to exclude any illegal clients but also to a restriction method which permits father and mother of a family to access a content stored in the father's personal computer while not permitting their child to access it.
There exists some server which has a function of collecting content information from other server on the home network and providing the collected content information to clients to share that content information. FIG. 9 shows a network AV system 1 having the content information sharing function. In this network AV system 1, a server SV1, server SV2 and client CL are connected through LAN on the network. The server SV1 stores content A in its content database and the content information X of the content A in its content information database. The server SV2 stores content B in its content database and the content information Y of the content B in its content information database. The servers SV1, SV2 share content information X and content information Y of the contents A, B The server SV2 and client CL are registered in the access permission information of the server SV1 so that the server SV1 permit access from the server SV2 and the client CL. Only the server SV1 is registered in the access permission information of the server SV2 so that the server SV2 permits only access from the server SV1.
When a client CL requests the server SV1 for content information, content information X+Y is returned to the Client CL (arrow 1 in FIG. 9). That is, the client CL can select a content to be reproduced from the contents A or B. If the content A is reproduced in the client CL, the content A is distributed from the server SV1 because the content A is stored in the sever SV1 which permits the client CL to access itself and the content CL can reproduce the content A. However, when the client CL reproduces the content B, even if the client CL requests the server SV2 for distribution of the content B (arrow (2) in FIG. 9), the server SV2 cannot distribute the content B to the client CL because the server SV2 does not permit access from the client CL (arrow (3) in FIG. 9). In a conventional server client system, the client CL can acquire content information Y of the server SV2 through the server SV1 although the client CL is not permitted to access the server SV2. Then, even if the client CL attempts to reproduce the content B based on the content information Y, it cannot acquire the content B from the server SV2 because the client CL is not permitted to access the server SV2, and finally the content B cannot be reproduced.